In connection with the beginning boom of low-rise housing construction, there is an active search for materials, the use of which makes it possible to build a house cheaply and technologically while achieving high operational properties. Such material exists and is already used in construction and is called thermal modification wood. This is wood, impregnated with a modifier solution (mainly carbamide), dried under variable pressure and heat treated in order to acquire and consolidate the desired properties.
Why wood? Because indoors, wood renews up to 30% of air per day, and the natural properties of this material allow it to give up accumulated moisture in dry weather, and to absorb its surplus in wet weather. Wooden houses are characterized by a special microclimate and a high level of comfort even without the use of additional air conditioning. Regarding density, the strength properties of wood are comparable to the properties of metals, and the thermal insulation properties are beyond competition with other types of building materials.
Why carbamide? A carbamide solution in water, due to the small size of carbamide molecules, is able to penetrate into the cells of the wood substance and soak through the wood blank of any thickness. carbamide, under the influence of temperature and pressure, reacts with such components of the wood substance as lignin and hemicelluloses and, without violating the macrostructure of wood, changes the chemical structure of these components with the formation of substances similar to carbamide resins used in the manufacture of modern plate materials.
Due to this, the wood becomes more durable and solid, does not lend itself to microorganisms (mold, fungi) and chemicals, and additives compatible with the modifier can make it fully or partially hydrophobic and non-combustible. At a certain stage of the technological process, modified wood becomes plastic and can easily deform under the influence of temperature and pressure. Carbamide is environmentally friendly, as it is chemically neutral in terms of its effects on humans and animals and is even used as a feed additive for cattle.
The technological process of thermal modification wood:
- through impregnation of the workpiece with an aqueous solution of modifier,
- and heat treatment.
If increased strength or hardness of thermal modification of wood (TMOF) is required, or the product is given a given shape or profile, then heat pressing, bending or rolling of dried wood is carried out.
As a result, TMOF sets the design, strength and operational properties necessary for the consumer, presented in the table. The source wood species does not significantly affect the final properties of the modified wood and therefore it is economically feasible to use cheap non-timber wood for modification.
Standard equipment manufactured by the industry can be used: heated baths or autoclaves for impregnation, convective or vacuum drying chambers, heat treatment chambers with a temperature of up to 200 ° C. For pressing, these are hydraulic presses with heated plates, bending equipment for bending, thermo-rolling plants with specially made profiled rolls. Special installations for thermal modification of wood have been tested, so far on a pilot scale, which allow all stages of modification to be carried out without reloading the workpieces, compacting the workpieces during drying, and even giving them the desired profile at the drying stage – for example, a groove and a tenon for a building beam. The use of such plants greatly reduces the modification time and wood processing costs.
The use of products from thermal modification of wood in the construction industry can be so diverse and almost universal that it is difficult even to answer the question: where is TMOF inefficient? However, we begin to “dance from the stove.” It is possible to make TMOF non-combustible, moreover, there are samples of such wood, and if they are compacted to 1500-2000 kg / m3, then from such “wooden bricks” you can add a stove or fireplace. Would be willing …
Next is the foundation. Since TMOF is very durable, not susceptible to decay, to the action of microorganisms and chemical reagents, and also non-combustible – the manufacture of a columnar or strip foundation from it suggests itself. Modified wood has been used as a formwork for pouring foundations or walls since the 80s and even entered into SNIPs. Due to its strength, thermal and chemical resistance, it can be used as a material of molds for the manufacture of concrete and other building mixtures.
The rounded log and timber from TMOF, manufactured in the pilot industrial version of the wood modification, are distinguished by the fact that they do not need to grind a bowl-shaped longitudinal profile on a log or a tenon and groove on a timber – this can be pressed out in the installation during the drying process. So the log was eaten with a diameter of 200 mm, a length of 2.5 m in a freshly cut state with a humidity of 85%, a density of 450 kg / cubic meter, with all the disadvantages inherent in this breed (litter knots, low bio-fire-moisture resistance) after 77 hours of treatment in the installation following properties:
- humidity 8%;
- density 630kg / cubic meter .;
- fire resistance is increased by 50%, and when applying special additives to the modifying solution, the log does not support combustion at all;
- moisture resistance is increased by 30% (more – when applying special additives to the modifier);
- MD is not affected by biohazards (mold, fungi, bugs, etc.);
- lumpy knots are pressed in and fused;
- on the log, a groove and a comb can be pressed out for articulation when assembling the log house (tested – 15 mm deep and 25 mm wide);
- wood texture is pronounced, the color can be changed from golden to dark brown throughout the thickness.
It should be noted that the house from such a log or bar looks very beautiful, it does not need external and internal decoration, as well as additional preventive measures. Shrinkage of the house after assembly does not occur, since the log or beam is dried during modification to 10-12%.
The beam does not “lead”, the strength depends on the degree of compaction of the wood, so it makes no sense to make glued beams from TMOF, reducing the cost. Beams, arches, trusses, etc., can be made of timber, that is, this is a very promising material for frame housing construction.
For frame house building, it is also possible to produce wall panels by thermo-compression molding. For this purpose, a contour mold of the required size is made of metal, for example steel 3, into which a packet of specially made MJMD rails of the same thickness is laid out “in a spacer”.
A special preparation of a package of rails consists in the fact that by machining (drilling and grooving) inside the package, a system of hollow channels is created, forming a grating inside the shield, which is filled with a foam able composition before pressing. The composition is a mixture of TMOF sawdust and a carbamide resin with a porophore, which cures when the pressing temperature is reached. A cushioning metal sheet is placed on the package of blanks for the manufacture of the shield or, if it is required to obtain a relief surface, a stencil. A thermal compression liner is laid out on top, consisting of segments of a special material with a large coefficient of thermal expansion.
When heated, the liner increases in volume much more than the metal limiting circuit and thereby creates the pressure necessary for sealing the shield from MHD (up to 30 MPa). The form closes with an interference fit with a punch in which, as in the matrix, there are heaters. When heated, the board is pressed and an internal reinforcing grate is formed, which during operation of the wall board or panel does not allow warping and changing the set dimensions.
In this way, it is possible to produce parquet boards, decorative panels, door leaf’s of any size in one pressing cycle. Parquet made of thermal modification of wood is characterized by increased hardness and wear resistance, dimensional stability. On a parquet board, you can apply a flat decorative image similar to intarsia, and even an image with a holographic effect. The image applied to the shield and the color change of the MXMD during pressing conceals a mismatch in the texture of neighboring battens when typing the shield.
From TMOF it is possible to make door and window blocks, molded products, elements of decoration. Since the modified wood bends well before heat treatment, it is possible to make arched elements of windows or doorways, bent handrails for stairs and other structural and decorative building elements with bending.
By introducing special additives into the modifier, you can get a waterproof TMOF, from which you can make garden gazebos and furniture, tiles and boards for garden paths, and by pressing – tiles to cover the roofs. The durability of these products is not inferior to analogues of polymeric materials, and the natural design of wood does not need protective and decorative coatings.
The production of products from thermal modification of wood can be introduced at any woodworking enterprise, for this you only need to equip it with special equipment for modifying wood. The basic type of equipment is an autoclave, which can be re-profiled by using the auxiliary services of the enterprise to make a plant for modification. This new innovative technology and equipment is not yet commercially available even abroad. But judging by the rapid development of thermal wood technology and a fairly wide range of equipment, the TMOF technology will take its rightful place in the woodworking industry in the coming years, and the products from the TMOF in the construction industry.